There has been a demand to measure various physical quantities mainly in the field of construction since before. Examples of the physical quantities include length, area, angle, volume, levelness, and the like. Examples of instruments for measuring these physical quantities include a measuring rod, a ruler, a measuring tape, a laser rangefinder, and the like, which measure a length, a protractor, a set square, a transit, and the like, which measure an angle, and a steel square, a level gauge, a plumb bob, and the like, which measure levelness and verticalness.
However, each of these instruments is dedicated to measuring a specific physical quantity. Taking the case of measuring length with a measuring tape, it is easy to measure the distance between specified two points and read the numerical value of the distance. However, it is difficult to perform measurement only with a measuring tape in “the case of determining the point vertically away from a wall by 2 meters”, “the case of determining the point vertically away from a floor by 1 meter”, and the like. In these cases, it is necessary to use a measuring tape in combination with a steel square, a plumb bob, or the like, and work of simultaneously using a plurality of instruments is extremely complicated. There are many other such cases, and there is a problem that although an instrument dedicated to a specific use is highly convenient for that use, it is not considered to use the instrument in combination with another instrument.
In addition, similarly, taking a measuring tape as an example, when the distance between specific two points is measured, in the case where the distance is beyond arm's reach of a human, work of fixing the origin of the measuring tape to one of the two points and then pulling the measuring tape toward the other point is necessary. Usually, a component for assisting fixation is attached to the origin of a measuring tape; however, the component is not versatile, and some arrangement is necessary for fixation of the origin in many cases. Then, after the length is measured, it is necessary to release the fixed origin of the measuring tape. Therefore, two steps, fixation and release of the origin, are necessary.
Furthermore, since a measurer himself intending to measure the distance has to go back and forth between two points at least once, man-hours taken for movement of the measurer cannot be ignored when the distance between the two points becomes large. In addition, it is difficult to linearly unroll the measuring tape other than by movement of the measurer in a case where a gap or the like exists between the two points.
Especially, like in the case of DIY (Do It Yourself), in the case where a worker carries out such a measurement by himself on site, the worker encounters the above difficulty.
As described, there is also the problem that man-hours of arrangements and movement of a measurer and the like, other than measuring work, which cannot be ignored, exist.
Regarding the problem associated with direct measurement of the above-described physical quantity by means of a dedicated instrument, since it is also possible to measure the three-dimensional coordinate values of the point to be a reference of physical quantity calculation and to calculate the physical quantity on the basis of the coordinate values, applying of a three-dimensional coordinate measurement technique to physical quantity calculation has been considered from the viewpoint of reduction in man-hours.
Conventionally, as techniques for measuring three-dimensional coordinates, a stereo camera (optical type), a mechanical type, a laser scanning type, and the like are general methods.
The stereo camera (optical type) is a camera configured to be able to measure distances in the vertical and horizontal directions and the depth direction with respect to the camera by simultaneously imaging an object from a plurality of different directions.
In the mechanical type, a contact or noncontact probe is mounted on the leading end of an articulated or linear motion mechanism, and a measurement target object is subjected to point measurement or line measurement by means of the probe, and therefore, three-dimensional coordinate values are calculated using the rotation angle of each joint axis in the case of the articulated motion mechanism, or the linear position of each axis in the case of the linear motion mechanism.
In the laser scanning type, three-dimensional coordinate values are calculated by determining the distance and the angle to the measurement target point according to the time taken for a laser beam to go back and forth and the projection direction of the laser beam.
In addition, there are various methods using radio waves, ultrasonic waves, and the like.
The inventor examined various methods and judged that an optical pattern projection type is excellent for usage which requires accuracy and strength against disturbance. Techniques for measuring two-dimensional coordinate values using an optical pattern are described in JP 2002-082763 A, and the like.